In recent years, following the strengthening of environmental regulations, high fuel consumption reducing properties have been required for engine oils. For this reason, there have been made efforts for blending a molybdenum compound, such as molybdenum dithiocarbamate (MoDTC), etc., in a lubricating oil composition, thereby reducing a metal-to-metal friction coefficient.
The molybdenum compound, such as MoDTC, etc., exhibits a friction-reducing effect in a relatively high temperature region of 80° C. or higher. Examples of the lubricating oil composition having a molybdenum compound blended therein include those disclosed in PTL 1.
Meanwhile, in order to inhibit the formation of a deposit in the inside of an engine at the time of high-temperature operation and to prevent the accumulation of a sludge, a metal-based detergent, such as a calcium detergent, etc., is added in the lubricating oil composition (see, for example, PTL 2).